A semiconductor device such as an LED or a power module has a structure in which a semiconductor element is bonded onto a circuit layer formed of a conductive material.
In a power semiconductor element for controlling the high power used for controlling wind power generation, electric cars, and hybrid cars, since the power semiconductor element has a significant heating value, a power module substrate including a ceramic substrate formed of AlN (aluminum nitride) or Al2O3 (alumina) and a circuit layer formed by bonding a metal plate having excellent conductivity to one surface of this ceramic substrate has been widely used as a substrate for mounting the power semiconductor element, in the related art. A substrate in which a metal layer is formed by bonding the metal plate to the other surface of the ceramic substrate is also proposed as a power module substrate.
Patent Document 1, for example, discloses a power module substrate in which a first metal plate and a second metal plate configuring a circuit layer and a metal layer are set as copper plates and the copper plates are directly bonded to a ceramic substrate by a direct bonding copper (DBC) method. In this DBC method, the generation of liquid phases is caused at interfaces between the copper plates and the ceramic substrate using a eutectic reaction between copper and copper oxide, and the copper plates and the ceramic substrate are bonded to each other.
In addition, Patent Document 2 discloses a power module substrate in which a circuit layer and a metal layer are formed by bonding copper plates to one surface and the other surface of a ceramic substrate. In this power module substrate, the copper plates are bonded to one surface and the other surface of the ceramic substrate by arranging the copper plates with a Ag—Cu—Ti-based brazing material interposed between the ceramic substrate and the copper plates and performing heating treatment (so-called an active metal brazing method). In this active metal brazing method, since a brazing material containing Ti which is an active metal is used, wettability of a melted brazing material and the ceramic substrate is improved and the ceramic substrate and the copper plates are successfully bonded to each other.